Battery management systems that rely on external cell performance parameters, such as voltage, current, and temperature, to determine state-of-charge (SOC) and/or state-of-health (SOH) result in conservative overdesign to manage the uncertainty in battery SOC and/or battery degradation with aging. This reliance on conservative overdesign of batteries has affected the widespread adoption of clean technologies, such as electric vehicles and power grid storage, by providing less accurate estimations regarding SOC and SOH. Conservative overdesign of batteries arises in part because the battery state cannot be fully understood from external parameters alone.
Some external methods for determining the SOC and SOH of battery cells include electrochemical impedance spectroscopy (EIS), neutron radiography and optical microscopy. These methods have been ineffective for mass production and distribution due to the inability to work properly during non-equilibrium states for EIS and the need for additional bulky and expensive equipment for neutron radiography and optical microscopy. Another method involves embedding MEMS temperature sensors in lithium-ion cells; however, these methods suffer from electromagnetic interference noise issues and the need for dedicated analog wires in each cell.